Carrier Trunk Full

What Causes This Error

All concurrent call channels on the outbound carrier trunk are in use. New outbound calls are being rejected with 503 Service Unavailable or 503 All Circuits Busy responses. Caused by insufficient concurrent call channels purchased from carrier, a burst of simultaneous dial attempts exceeding trunk capacity, or a carrier-side issue.

How to Fix It

• Check active channel count: asterisk -rx ‘core show channels’ | wc -l

• View active calls by trunk: asterisk -rx ‘sip show channels’ | grep TRUNK_NAME

• 3 Check carrier 503 responses in SIP log: grep 503 /var/log/asterisk/messages

• 4 Temporarily reduce dial level to decrease concurrent calls

• 5 Contact carrier to verify channel allocation and request emergency expansion

• Review asterisk -rx ‘sip show peers’ for trunk status

• 7 Implement concurrent call cap in dialplan to prevent exceeding trunk limits

How to Prevent It

Monitor channel utilization and set dial level to stay under 80% of trunk capacity. Purchase channel capacity that is 125-150% of expected peak usage. Set max_hopper_calls to prevent runaway dialing. Get carrier SLA with guaranteed channel expansion capability.

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